1. Field of the Invention
The invention relates to a control apparatus for an internal combustion engine where intake valve timing and exhaust valve timing can be adjusted and fuel is injected into an intake passage, which calculates an index that indicates the amount of fuel adhering to the wall surface of an intake passage based on the operating state of the engine, and controls the amount of fuel to be injected based on the index.
2. Description of the Related Art
In internal combustion engines where fuel is injected into an intake passage from a fuel injection valve, part of the injected fuel adheres to the wall surface of the intake passage. The amount of fuel adhering to the wall surface is not constant, and varies depending on the operating state of the internal combustion engine. Accordingly, when the amount of fuel adhering to the wall surface increases, the amount of fuel supplied to a combustion chamber is less than the amount of fuel injected from the fuel injection valve. When the amount of fuel adhering to the wall surface decreases, the amount of fuel supplied to the combustion chamber is greater than the amount of fuel injected from the fuel injection valve. As a result, the air-fuel ratio estimated based on the amount of injected fuel and the amount of intake air is deviated from the actual air-fuel ratio. This deviation of the estimated air-fuel ratio from the actual air-fuel ratio may cause problems relating to the output of the engine and exhaust gas discharged from the engine.
The amount of fuel adhering to the wall surface is greatly influenced by the valve overlap between the intake valve and the exhaust valve, which may cause exhaust gas to flow back to the intake passage. Therefore, in an internal combustion engine where the valve overlap can be adjusted, the deviation of the estimated air-fuel ratio from the actual air-fuel ratio needs to be prevented. Thus, for example, Japanese Patent Application Publication No. JP-A-11-36936 (hereinafter, referred to as No. 11-36936) and Japanese Patent Application Publication No. JP-A-8-261034 (hereinafter, referred to as No. 8-261034) describe control apparatuses which estimate an index that indicates the amount of fuel adhering to the wall surface of an intake passage based on the valve overlap amount, and an advance angle of the intake valve timing corresponding to the valve overlap amount; and correct the amount of fuel to be injected based on the amount of fuel adhering to the wall surface of the intake passage.
However, the control apparatuses described in No. 11-36936 and No. 8-261034 execute the control on the assumption that only the intake valve timing is adjusted, and the exhaust valve timing is not adjusted. Therefore, consideration is not given to the influence of the valve timing on the amount of fuel adhering to the wall surface of the intake passage in the case where both the intake valve timing and the exhaust valve timing can be changed even when the overlap amount remains the same.
The intake valve timing and the exhaust valve timing are physical quantities different from each other. Thus, in the case where the technologies described in No. 11-36936 and No. 8-261034 are applied to the internal combustion engine where both the intake valve timing and the exhaust valve timing are adjusted, the behavior of the amount of fuel adhering to the wall surface of the intake passage may be different from the estimated behavior, which reduces the accuracy in controlling the amount of fuel to be injected.